Whether you hunt with a conventional bow, compound bow, crossbow or rifle.... do you carry a back up and/or a spare parts kit? And do you carry a small tool kit of the required Allen wrenches, screwdrivers and maybe a small rat tail file?
RIFLES: For the most part... any malfunction with a rifle is usually the scope due to a sharp blow knocking the cross hairs off, gas leak from the tube which is the primary cause of fogging within the interior of the scope.
I have witnessed the front of a Redfield scope snapping off at the front flare in extreme cold weather.... when the hunter fell while wearing Bearpaw snowshoes for the first time. That was the end of his Caribou hunt.
A spare scope or even having a back up rifle is a must.
Many will go thru' a few scopes and most have the old ones laying around. Toss one of them in your spare parts kit.
Another problem I witnessed is the feed on a new bolt action Savage Model 110 MCL .338 Mag. As the bolt was pulled back and the spring pushed a round up and the bolt was beginning to be pushed forward.... the spring kicked the round completely out of the rifle. Not good when time element will allow only one shot.
BOWS: Generally spare parts kit for bows should contain a new string.
Conventional bows require little in the way of spare parts, but not so with compounds and crossbows. I always carry a spare string, spare sight, spare rest, small portable bow compressor, and anything I might need for anything imaginable to go wrong.
Spare sight is a must. One hunter I know was carrying his bow by the string thru Sage brush. A dry limb entered his sight and shredded the pins. He did not have a spare. I always have a bow sling, with cover, whenever transporting my bow and do not pull it off until in my blind or where ever.
Strings can get damaged... rests, especially fall away, can have the smaller Allen screws come loose like the screw that holds the top bar that keeps the arrow from falling out.
I always carry a "Whisker Biscuit" type rest as a spare. They are easy to replace and mount as opposed to the Fall Away set up.
Use your imagination on what could go wrong with the weapon of your choice.... and plan accordingly of what could possible go wrong.
Not planning ahead could make the difference between having an enjoyable hunt.... or having to return home or to the nearest town for repairs or parts.
Stay safe n' good huntin'...